1. Field of the Invention
The present invention relates to a circuit board cabinet having a plurality of shelves arranged therein one above another for receiving circuit boards, and more particularly to a circuit board cabinet having heat-shielding capability.
2. Description of the Related Art
A communication apparatus for connecting a large number of communication lines is required to incorporate a large member of circuit boards in dependence on the number of the communication lines, etc. The communication apparatus of this kind is typically housed in a cabinet.
FIG. 10 is an exploded perspective view showing an outline of the construction of a conventional cabinet of a communication apparatus. The cabinet 60 has a power supply unit 62 arranged at the bottom of a frame 61 thereof. A plurality of shelves 63 (only one of the shelves 63 is shown in the figure) are arranged in the frame 61 one above another. Each of the shelves 63 has a large number of circuit boards 64 fitted therein in parallel with each other. Further, a front cover plate 65 is attached to a front end of the shelf 63 such that it can be opened and closed. Top and bottom faces of the shelf 63 are open to ensure ventilation. A heat shield unit 66 is arranged immediately above each of the shelves 63.
FIG. 11 is a perspective view showing details of the construction of the conventional heat shield unit 66. A housing 661 of the heat shield unit 66 has a top face 662, a bottom face 663, and a rear face 664, which are all open. A front face 665 of the housing 661 is formed with lots of vent holes 665a for taking in air flowing toward the front face 665. In the housing 661, there is mounted a heat guide plate 666 which extends obliquely downward from an upper end of the rear face 664 to a lower end of the front face 665 in a manner dividing a space within the housing 661 into upper and lower portions. The air flowing into the housing 661 through the front face 665 is guided by the oblique heat guide plate 666 and discharged via the open top face 662. On the other hand, air flowing in via the open bottom face 663 is guided by the underside of the oblique heat guide plate 666 and discharged via the open rear face 664.
FIG. 12 illustrates streams of air flowing within the cabinet 60 in which the shelves 63 are mounted. The air flowing into each of the heat shield units 66 through the front face 665 thereof is guided upward by the heat guide plate 666 and passes through the shelf 63 immediately above the heat shield unit 66. The air cools the shelf 63 while passing therethrough. After cooling the shelf 63, the air is guided by the heat guide plate 666 in another heat shield unit 66 immediately above the shelf 63 and discharged backward from the cabinet 60.
However, it is obligatory that the cabinet 60 of this kind is provided with a sufficient self-fire extinguishing capability so as to prevent a fire from spreading to other devices in case the fire occurs within the cabinet.